Diabetes is characterized by chronic hyperglycemia. There are 2 forms of the disease, insulin dependent (Type I) and non-insulin dependent (Type II). The disease process associated with both Type I and Type II includes a microvascular pathology that can result, for example, in blindness, renal failure and nerve damage. In addition, an accelerated atherosclerotic macrovascular pathology can affect arteries supplying the heart, brain and lower extremities. (See, for example, Brownlee, Nature 414:813 (2001).)
Type I diabetes is caused by the autoimmune destruction of insulin-producing pancreatic β cells. A large body of evidence supports the concept that the antigen-specific, T cell-mediated infiltration of inflammatory cells to the pancreas leads to the generation of reactive oxygen species (ROS) [superoxide, (O2.−), hydroxyl radical (.OH), nitric oxide (NO.), peroxynitrite (ONOO−)], and pro-inflammatory cytokines (TNF-α, IL-1β (interleukin 1β) and IFN-γ (interferon γ) (Rabinovitch et al, Endocrinology 137:2093-2099 (1996), Mandrup-Poulsen, Diabetologia 39:1005-1029 (1996), Eizirik et al, Diabetologia 39:875-890 (1996), Mandrup-Poulsen et al, Eur. J. Endocrinol. 134:21-30 (1996)). Synergistic interaction between ROS (reactive oxygen species) and these cytokines results in the ultimate destruction of the pancreatic β cells.
Locally produced ROS are involved in the effector mechanisms of β cell destruction (Rabinovitch et al, Endocrinology 137:2093-2099 (1996), Mandrup-Poulsen, Diabetologia 39:1005-1029 (1996), Eizirik et al, Diabetologia 39:875-890 (1996), Grankvist et al, Biochem. J. 182:17-25 (1979), Kroncke et al, Biochem. Biophys. Res. Commun. 175:752-758 (1991), Corbet et al, J. Clin. Invest. 90:2384-2391 (1992)). In vitro, T cell and macrophage cytokines such as IFN-γ, IL-1β and TNF-α (tumor necrosis factor-α) induce the production of ROS by β cells. In addition, ROS either given exogenously or elicited in β cells by cytokines lead to β cell destruction (Lortz et al, Diabetes 49:1123-1130 (2000)). This destruction appears to ultimately be caused by an apoptotic mechanism (Kurrer et al, Proc. Natl. Acad. Sci. USA 94:213-218 (1993), O'Brien et al, Diabetes 46:750-757 (1997), Chervonski et al, Cell 89:17-24 (1997), Itoh et al, J. Exp. Med. 186:613-618 (1997)). β cells engineered to over-express antioxidant proteins have been shown to be resistant to ROS and NO. (Grankvist et al, Biochem. J. 199:393-398 (1981), Malaisse et al, Proc. Natl. Acad. Sci. USA 79:927-930 (1982), Lenzen et al, Free Radic. Biol. Med. 20:463-465 (1996), Tiedge et al, Diabetes 46:1733-1742 (1997), Benhamou et al, Diabetologia 41:1093-1100 (1998), Tiedge et al, Diabetes 47:1578-1585 (1998), Tiedge et al, Diabetologia 42:849-855 (1999)). Furthermore, stable expression of manganese superoxide dismutase (Mn-SOD) in insulinoma cells prevented IL-1β-induced cytotoxicity and reduced nitric oxide production (Hohmeier et al, J. Clin. Invest. 101:1811-1820 (1998)). Finally, others have shown that transgenic mice with β cell-targeted over-expression of copper, zinc SOD or thioredoxin are resistant to autoimmune and streptozotocin-induced diabetes (Kubisch et al, Proc. Natl. Acad. Sci. USA 91:9956-9959 (1994), Kubisch et al, Diabetes 46:1563-1566 (1997), Hotta et al, J. Exp. Med. 188:1445-1451 (1998)).
SOD mimics have been designed with a redox-active metal center that catalyzes the dismutation of O2− in a manner similar to the active metal sites of the mammalian Cu, Zn- or Mn-containing SODs (Fridovich, J. Biol. Chem. 264:7761-7764 (1989), Pasternack et al, J. Inorg. Biochem. 15:261 (1981), Faulkner et al, J. Biol. Chem. 269:23471-23476 (1994), Batinic-Haberle et al, J. Biol. Chem. 273:24521-24528 (1998), Patel et al, Trends Pharmacol. Sci. 20:359-364 (1999), Spasojevic et al, Inorg. Chem. 40:726 (2001)). The manganese porphyrins have a broad antioxidant specificity, which includes scavenging O2− (Batinic-Haberle et al, Inorg. Chem. 38:4011 (1999)), H2O2 (Spasojevic et al, Inorg. Chem. 40:726 (2001), Day et al, Arch. Biochem. Biophys 347:256-262 (1997)), ONOO−, (Ferrer-Sueta et al, Chem. Res. Toxicol. 12:442-449 (1999)), NO− (Spasojevic et al, Nitric Oxide: Biology and Chemistry 4:526 (2000)) and lipid peroxyl radicals (Day et al, Free Radic. Biol. Med. 26:730-736 (1999)). SOD mimics have recently been found to rescue vascular contractility in endotoxic shock (Zingarelli et al, Br. J. Pharmacol. 120:259-267 (1997)), protect neuronal cells from excitotoxic cell death (Patel et al, Neuron 16:345-355 (1996)) and apoptosis (Patel, J. Neurochem. 71:1068-1074 (1998)), inhibit lipid-peroxidation (Day et al, Free Radic. Biol. Med. 26:730-736 (1999), Bloodsworth et al, Free Radic. Biol. Med. 28:1017-1029 (2000)), block hydrogen peroxide-induced mitochondria) DNA damage (Milano et al, Nucleic Acids Res. 28:968-973 (2000)), and partially rescue a lethal phenotype in a manganese superoxide dismutase knockout mouse (Melov et al, Nat. Genet. 18:159-163 (1998)). The ability of the SOD mimics to scavenge a broad range of ROS allows for their utilization in inflammatory diseases.
The present invention provides a pharmacological approach to protect β cells from the T cell mediated ROS and cytokine destruction associated with autoimmune diabetes by employing a synthetic metalloporphyrin-based superoxide dismutase mimic. The invention also provides a method of improving survival of pancreatic β islet cells following transplantation.